The present invention relates to silicone compositions which, when cured, exhibit pressure sensitive adhesive properties and are of an elastomeric nature.
Silicone pressure sensitive adhesives have found use in medical devices which adhere to a patient's skin, such as transdermal drug delivery patches. Transdermal drug delivery patches are typically composed of a non-permeable cover which covers a reservoir of drug. The cover typically has a rim extending beyond the reservoir which has a silicone pressure sensitive adhesive (SPSA) on the surface which is to be applied to the patient's skin. The device also has, attached to the SPSA, an impermeable backing layer having a release coating thereon, the backing layer being removed prior to adhering the device to the skin. The reservoir may be a material (e.g. elastomeric) impregnated with the drug, ofter referred to as a "matrix", or it may be a solution of the drug. Between the reservoir and the patient's skin, there is ofter a membrane through which the drug travels from the reservoir to the patient. This membrane may be formed of a silicone pressure sensitive adhesive.
To reduce the number of component parts and make assembly easier, it is desirable to have a material that would provide both pressure sensitive adhesive and elastomeric properties which could be used to form either a membrane or a matrix for transdermal drug delivery devices. Current volatile solvent-containing SPSA's often exhibit formation of bubbling when cured into thick sections as would be needed for the matrix of a matrix type transdermal drug delivery device, resulting in a non-uniform product. Some current SPSA's have also been found to lose cohesiveness and, ofter, detackify with the addition of many drugs and/or excipients used in the pharmaceutical industry, such as nonionic surfactants, e.g. isopropylpalmitate. The inclusion of drugs or excipients ofter results in dissolving the SPSA's, causing them to flow and lose their original shape even at room temperature.
Some prior art SPSA's have also been known to aggressively adhere to substrates, especially with age, which is usually undesirable, resulting in increased difficulty in removal from the substrate, whether it be, e.g., a patient's skin or paper. Therefore, there is need for SPSA's having controllable aggressiveness.
In the past, activity at the National Aeronautics and Space Administration (NASA) Langley Research Center has focused on forming PSA's having some elastomeric quality. Such activity is disclosed in U.S. patent application Ser. No. 569,536, entitled "Structural Pressure Sensitive Adhesives" filed Jan. 12, 1984, now abandoned, as NASA Case LAR-13,270-1. The specification and abstract of this application was made public when its public availability was announced in 1984 in NASA Patent Abstracts Bibliography, NASA Publication No. SP-7039(31), as Accession No. N84-32532. The application discloses the blending of an intermediate molecular weight pressure sensitive silicone adhesive with a silicone system which generally cures with a catalyst to a rubber tack-free state, to form a pressure sensitive silicone adhesive. The application discloses as a specific example, the blend of SR6574 (described in the application as a liquid, tacky silicone gum or uncrosslinked resin system which contains 44-46% volatiles and is available from General Electric under the tradename Silgrip), RTV 560, (described as a liquid silicone rubber also available from General Electric), and a catalyst employed to cure the RTV 560 portion but not cure the SR6574 component.
The application also discloses that Dow Corning RTV 3120 (with catalyst) and "Silastic LS420 Gum (a Dow Corning tradename fluorosilicone rubber)" may be substituted, respectively, for the RTV 560 and SR6574, and that General Electric's SR595, described as another pressure sensitive adhesive, may be employed in lieu of the SR6574. Additionally, the application discloses that silicone resins which cure with platinum compounds via .tbd.SiH to .tbd.SiVi or acetoxy- or alkoxy-containing silicones which cure with moisture may be employed as the curing resin.
As disclosed in Dow Corning Corporation's Product Brochure Form No. 10-052B-85 (1985), DOW CORNING.RTM. 3120 is a two-part room temperature vulcanizing (RTV) silicone rubber which can be catalyzed by stannous octoate or dibutyl tin dilaurate. As disclosed in Dow Corning Corporation's Product Brochure Form No. 17-325-81 (1981), SILASTIC.RTM. LS-420 Fluorosilicone Gum is a silicone polymer with methyl, trifluoropropyl, and vinyl substituents.
The PSA compositions taught in the NASA application contain volatile solvents. The presence of the volatile solvent can result in bubbling in thick sections prepared from the PSA.